This invention relates to a valve driving apparatus in an internal combustion engine, chiefly in a four-cycle machine for a vehicle. The particular type of engine has plural valve stems disposed in a cylinder head on an upper portion of a main body of the engine. The stems are aligned radially about the cylinder head having the intersection of their longitudinal axes substantially coinciding with a center of curvature of an upper wall surface of a combustion chamber.
A conventional valve driving apparatus is constructed with each of valve stems being driven by being pushed directly by a swing movement of a corresponding rocker arm supported on a shaft which extends in parallel with a cam shaft. However, if such a structure is applied to an engine of the type having plural valve stems aligned radially about the cylinder head with the intersection of their longitudinal axes substantially coinciding with a center of curvature of an upper wall surface of a combustion chamber, it is difficult to align the locus plane of a swing movement of the rocker arm and a longitudinal axial direction of the valve stem. Therefore, there has been proposed an arrangement wherein a subsidiary rocker arm is interposed between a rocker arm and a corresponding valve stem. The locus plane of the swing movement of the subsidiary arm is aligned with the longitudinal axial direction of the valve stem so that the valve stem may be pushed therethrough in the longitudinal axial direction thereof by the rocker arm. It is desirable with this arrangement that a diametrical directional force acting on the valve stem at the time of swing movement of the subsidiary rocker arm is made as small as possible for improving the durability of the valve means.